1. Field of the Invention
The present invention relates to a wrapping device such as a wrapping bag or a wrapping container for housing an object, e.g. a food product, in a fluid-tight state, and more particularly to a wrapping device constructed of a laminate film formed by bonding of a plurality of synthetic resin sheet materials which are non-heat-fusible relative to each other.
2. Description of the Related Art
With a wrapping bag into which an object and a gas are introduced at one time, the bag may burst when subjected to an external force applied by e.g. vertical stacking of a plurality of bags. Further, the bag may burst also by vapor generated from the housed object when heated or vaporization of solid carbon dioxide housed within the bag together with the object for the purpose of its refrigeration. In this respect, a communicating hole may be formed in the laminate film forming the wrapping bag. However, with such simple arrangement alone, while the communicating hole may discharge the air initially housed within the bag or the gas or vapor generated after the sealing of the bag, there may occur other inconvenience such as invasion of foreign substance through the communicating hole or invasion of oxygen through the same which results in undesirable oxidation of the housed object.
Moreover, when the food product as being sealed within the container is heated in a microwave oven, vapor generated from the product in association with the heating increases the gas pressure inside the container, and this increased gas pressure may burst open the laminate film acting as a cover or even the container body, so that the product may be destroyed and scattered inside the oven. In order to avoid this problem, it has been suggested to break open, before heating, a part or whole of the heat-fused portion between the container body and the cover or cut an opening in the laminate film so as to communicate the inside of the container with the ambience to allow escape of the vapor generated from the food product due to its heating. However, this method makes the heat cooking more troublesome. Also, if the user forgets to form such opening before heating and the food product as remained sealed within the container is heated, this will result in the burst of the cover or the container body.
Then, in order to prevent such inconvenience, the prior art has suggested use of an anti-reverse valve 51 as shown in FIG. 36 (e.g. Japanese laid-open utility model gazette No. 63-67443, Japanese laid-open utility model gazette No. 63-59838). This wrapping bag has its peripheral edges heat-sealed with leaving open an entrance opening 50. The anti-reverse valve 51 is inserted into the entrance opening 50 and then heat-fused to the same. The anti-reverse valve 51 consists of a planar tube portion 51A formed of a synthetic film and a film piece 51B also formed of the synthetic material. One end of the film piece 51B is bonded to one of opposing inner faces of the tube portion 51A and the other end of the film piece 51B is placed in close contact with the other inner face of the tube portion 51A. With this, a communicating passage is formed between the inner face of the tube portion 51A and the other end of the film piece 51B, to allow fluid inside the bag to be discharged to the outside.
However, the above-described conventional wrapping bag requires the anti-reverse valve 51 made of a synthetic resin film, in addition to the bag body. Moreover, the manufacturing process of this bag requires the step of heat-fusing the anti-reverse valve 51 to the entrance opening 50 with inserting and fixedly maintaining the former at a predetermined position of the latter. For this reason, it becomes difficult to effect the above-described heat-fusing step while charging the object into the bag in a continuous manner. Thus, the mechanism for automatic wrapping operation tends to be complicated, thereby to add to the production costs as a whole.
Furthermore, since the attaching position of the anti-reverse valve 51 is limited to the entrance opening 60 of the bag, the construction tends to impose undesirable restrictions on the designs of the shape of the bag.
The present invention attends to the above-described state of the art, and its primary object is to provide an improved wrapping device such as a bag or a container which may normally maintain good fluid-tight condition while allowing smooth discharging of the inner fluid or gas to the outside when necessary. The container device may also effectively resist invasion of e.g. germs if the device should be opened during its transportation or storage. The container also allows greater designing freedom in e.g. the discharging position of the fluid and the shape of the bag. And, this bag may be automatically manufactured at low costs.